Question

An ideal heat engine exhausting heat at ${77}^{o}C$ is to have $30\%$ efficiency. It must take heat at

• A. ${673}^{o}C$
• B. ${327}^{o}C$
• C. ${227}^{o}C$
• D. ${127}^{o}C$

Answer 1

Answer: (C)

${227}^{o}C$

The efficiency of the cycle is given as $\eta =1-\frac{T_2}{T_1}$. Here $T_1$ is the temperature of the source and $T_2$ is the temperature of the sink. . Thus we get $0.3=1-\frac{350}{T_1}$
or, $T_1=500K={227}^{o}C$